The field of the invention is camera cranes.
Camera cranes are used in the production of motion pictures, video, and television programs. Typically, a camera crane arm or boom is pivotably mounted onto a base. A camera is mounted on a camera platform at the front end of the arm. Counterweights on a counterweight platform or bucket at the back end of the arm are added to place the arm into a balanced, or near balanced equilibrium. The base may be a mobile dolly or platform.
The length of the arm is adjusted by adding or removing crane arm segments, which are bolted and/or pinned together to form in integral arm. The camera crane arm is preferably highly rigid, when assembled, to avoid inadvertent deflections of the camera as the camera crane arm is moved. For example, if the camera crane arm is not sufficiently rigid, rapid movements of the camera crane arm (as may be necessary to film a sequence having rapid movements) may result in flexing or whipping of the arm and camera, rendering the filmed sequence unusable. However, while a highly rigid camera crane arm is desirable, at the same time, the arm should be able to be assembled into a long length, to provide an adequate range of lens height, and the arm should be light weight and preferably compact, so that it can be readily stored, shipped, assembled and maneuvered. To make the camera crane arm more rigid, tensioning cables may also be used. Typically, the cables extend from various locations along the arm, to a cable truss extending above the central section of the camera crane arm, which is pivotably mounted on the crane arm base.
While these types of camera cranes have worked well in the past, certain disadvantages remain. Due to the geometry of the camera crane arm, bending deflection of the camera crane arm when loaded, and to the shifting position of the camera crane arm and cable truss, as the arm elevation is changed, the arm cannot be uniformly balanced purely via counterweights. For example, a camera crane arm may be balanced purely with counterweights, when the arm is in the horizontal position. However, as the arm is raised to elevate the camera, the center of gravity of the cable truss shifts rearwardly, bringing the arm out of balance and making the arm back-end heavy. Consequently, to return the arm to a horizontal position requires significant upward force at the back end or weight bucket of the arm. This requires the camera crane operators to do significant lifting, and to operate the crane with a higher level of care and skill. In addition, the arm becomes unstable, so that significant braking forces are needed to hold it in position.
Accordingly, it is in object of the invention to provide an improved camera crane arm having a system for better maintaining the camera crane arm in a balanced condition.
To these ends, a camera crane includes a support frame or U-frame. A camera crane center or post section is pivotably mounted to the support frame. A spring balancing system includes a spring link also attached to the support frame. A spring post is attached to the crane arm section. At least one spring is attached to both the spring post and to the spring link. With the spring link fixed in position, upward pivoting movement of the camera crane arm, which tends to make the crane arm back-heavy also simultaneously stretches the spring. The spring exerts a counter force which tends to negate the back-heavy condition of the camera crane arm. As a result, the camera crane arm remains more uniformly balanced, not withstanding the variations in forces which occur during changes in elevation of the arm.
Preferably, the spring link can be locked into a fixed position with a quick release pin, so that the spring force exerted by the spring counteracts the other forces tending to make the crane arm back heavy. Releasing the pin allows the spring link to pivot, in response to the spring force, thereby disengaging the spring counterbalancing system.
Spring posts are advantageously provided in front and in back of the spring link. Additional counterbalancing force can be provided by attaching multiple springs onto the spring link and spring posts.
The spring balancing system may be provided on one side, or on both sides of the camera crane arm.